1. Field of the Invention
The instant invention is directed to a process for cracking heavy carbonaceous liquid feedstock using hydrogen donor solvent derived from the feedstock. More particularly, the instant invention is directed to a process for cracking heavy carbonaceous liquid feedstock using a hydrogen donor solvent, derived from the feedstock, in a two-stage operation.
2. Background of the Prior Art
Until very recently, the cracking of heavy carbonaceous liquid feedstock by use of hydrogen donor solvent cracking was limited to either producing hydrogen donor solvent boiling above 370.degree. C. by (i) reacting polynuclear aromatics with hydrogen in the presence of a conventional hydrogenation catalyst to convert the polynuclear aromatics to polynuclear hydroaromatics or (ii) by providing an external source of hydroaromatic donor solvent or donor solvent precursor. The use of these high boiling donor solvents creates inherent difficulty in that they possess less hydrogen available per unit weight than hydrogen donor solvents boiling at lower temperature and that they either must be derived from an external source or be produced from the cracking of the subject feedstocks by the donor solvent cracking process.
Illustrative of prior art practice involving the use of heavy, i.e., high boiling hydrogen donor, solvents are the following:
U.S. Pat. No. 2,953,513, Langer, Sept. 20, 1960 employs heavy, that is, high boiling, solvents. The solvents employed by Langer are not native to the feedstock used in the instant invention in sufficient concentration to render them active as hydrogen donors. The key components in the feedstock disclosed by Langer cannot be readily produced from other hydrocarbon species.
U.S. Pat. No. 4,051,012, Plumlee, Sept. 27, 1977, discloses a process specific to cold feedstock which exhibit synergism between a quinone catalyst and oxygenated species that exist in coal-derived donor solvent. It is noted that the carbonaceous feedstocks of this invention are largely hydrocarbons that do not contain any significant quantity of oxygenated species.
U.S. Pat. No. 2,843,530, Langer, July 15, 1958, discloses the use of makeup hydrogen donor solvent derived from an external source such as tars, cyclic oils and lube oil extracts. Obviously, such a system does not provide the advantages of internally generated solvent. It is noted that this external derived hydrogen donor solvent does not include naphthalene, a very desirable precursor for hydrogen donor solvents.
U.S. Pat. No. 3,867,275, Gleim, Feb. 18, 1975, comments on the expense and difficulty of obtaining two-ring aromatic solvents, solvents of the type that make excellent hydrogen donors.
Gorin et al, Proc, 8th World Pet. Congress, Preprints Session No. PD10 (5), 44 (1971), discloses a highly aromatic solvent derived from a coal feedstock.
Representatives, also, of the state of the art are U.S. Pat. No. 3,849,287, Gleim, Nov. 19, 1974; U.S. Pat. No. 3,336,411, Benham, Aug. 15, 1967; U.S. Pat. No. 3,775,498, Thompson, Nov. 27, 1973; U.S. Pat. No. 2,585,899; Langhor's, Feb. 12, 1952; U.S. Pat. No. 3,504,045, Scharf, Mar. 31, 1970; U.S. Pat. No. 4,176,046, McConaghy, Nov. 27, 1979; U.S. Pat. No. 4,115,246, Sweany, Sept. 19, 1978; and U.S. Pat. No. 4,213,846, Sooter et al, July 22, 1980; Doyle, "Desulfurization Via Hydrogen Donor Reactions:, "Division of Petroleum Chemistry, ACS, Chicago Meeting, Aug. 24-29, 1975, p 165; Neavel, "Liquifaction of Coal in Hydrogen-Donor and Hydrogen Non-Donor Vehicles", Fuel, 1976, Vol. 55, July, p. 2-37; Carlson, "Thermal Hydrogenation", Ind. & Eng. Chem., Vol. 50, No. 7, p. 1067; "Aromatic Hydrocarbons"--pp. 230-236, Production and Separation of alkylnaphthalenes, Marshal Sittig, Editor, 1976, Noyes Data Corp., Parkridge, N.J.
A recent reference, U.S. Pat. No. 4,294,686, Fisher et al., Oct. 13, 1981, overcomes one of the principal problems of the prior art. That is, it provides for employing recycled hydrogen donor solvent having a boiling point below 370.degree. C. in the cracking of heavy carbonaceous liquids. However, when certain feedstocks are provided the process disclosed does not provide sufficient recycle solvent to maintain material balance for a continuous process.
To overcome this defect, a still more recent reference, U.S. patent application, Ser. No. 238,344 filed Feb. 22, 1980, now U.S. Pat. No. 4,363,716 overcomes this defect in the '686 patent. The application, assigned to the same assignee as the present application, discloses a liquid phase process, in total material balance with respect to recycled solvents, for cracking heavy carbonaceous liquid feedstocks using a hydrogen donor solvent having a boiling range of from 175.degree. to 300.degree. C.
This patent application represents a significant advance in the art. However, certain possibilities for improvement of the process of this application have been identified. In the process disclosed in application, Ser. No. 238,344, there is a reduction in coking compared to the disclosures of the prior art. However, there is still some tendency towards coking. In that the carbonaceous liquid feedstock of this invention have high coking propensity, and are difficult to upgrade by the processing steps of the prior art, there is still need for improvement in the processing of heavy carbonaceous liquid feedstocks.